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Home/DTC Codes/Mazda/CX-3/2016-2021 2.0L I4/P0401
P0401

EGR Flow Insufficient Detected

2016-2021 Mazda CX-3 2.0L I4

Moderate SeverityPowertrainGeneric (SAE)

Description

The EGR system is not flowing enough exhaust gas. This is one of the most common EGR codes.

Symptoms

  • Check Engine Light
  • Pinging under load
  • Failed emissions (high NOx)
  • Slight rough idle

Common Causes

  • Clogged EGR passages (most common)
  • EGR valve stuck closed
  • Clogged EGR tube
  • Faulty DPFE/MAP sensor
  • Carbon buildup in intake manifold

Diagnostic Steps

  1. Check EGR passages for carbon restriction
  2. Test EGR valve by applying vacuum (should open and idle should change)
  3. Inspect EGR tube between exhaust and valve
  4. Test DPFE sensor (Ford) or EGR position sensor
  5. Clean carbon from intake ports

Repair Notes

Clean EGR passages and valve. This is maintenance, not just a repair. Replace EGR valve if cleaning fails.

Related Codes

P0400Exhaust Gas Recirculation (EGR) FlowP0402EGR Flow Excessive Detected

Other Powertrain Codes

P0401 on Other Vehicles

Mazda 626

1993-1997 2.0L I4

Mazda 626

1993-1997 2.5L V6

Mazda 626

1998-2002 2.0L I4

Mazda 626

1998-2002 2.5L V6

Mazda Axela

2013-2019 1.5L I4 P5-VPS

Mazda Axela

2013-2019 2.2L I4 Diesel SH-VPTS

Mazda B2300

1994-1997 2.3L I4

Mazda B2300

2002-2009 2.3L I4

Common Questions

What does code P0401 mean on a 2016-2021 Mazda CX-3?

P0401 stands for "EGR Flow Insufficient Detected". The EGR system is not flowing enough exhaust gas. This is one of the most common EGR codes.

What are the symptoms of P0401 on a Mazda CX-3?

Common symptoms of P0401 include: Check Engine Light, Pinging under load, Failed emissions (high NOx), Slight rough idle.

What causes P0401 on a 2016-2021 Mazda CX-3?

Common causes of P0401 include: Clogged EGR passages (most common), EGR valve stuck closed, Clogged EGR tube, Faulty DPFE/MAP sensor, Carbon buildup in intake manifold.

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